The present invention relates to a printing apparatus for printing types with different impact forces in correspondence with characters that should be printed.
Conventionally, there is known a daisy wheel type printing apparatus which is equipped with a daisy wheel having a plurality of supporting plates which extend radially and each of which has a type at its end portion.
Among such printing apparatuses, there is a printing apparatus in which an impact force of a printing hammer is changed in accordance with a character to be printed in order to make the densities of the characters printed on a paper uniform. For example, in the case of printing a period "." having a small type area, the impact force of the printing hammer is set to be weak, while in the case of printing a character such as "W" or the like having a large type area, the impact force of this printing hammer is set to be large.
In such a printing apparatus, a rotation angle data and impact force data corresponding to each character are stored in a memory; the printing wheel is rotated into a desired location on the basis of the rotation angle data in accordance with an input character code; and the type is printed by the printing hammer on the basis of the impact force designated by the corresponding impact force data. In this manner, a desired character can be printed on paper.
For instance, in a certain printing apparatus, there are used a first memory for storing the rotation angle data of the printing wheel corresponding to each character code and a second memory for storing the impact force data of the printing hammer corresponding to each character code. When a character code is inputted, a central processing unit (CPU) reads out, individually and respectively, the rotation angle data and impact force data corresponding to this input character code from the first and second memories. The CPU then supplies them to a printing wheel driver and a printing hammer driver. This makes it possible to print each character with a desired impact force. However, the CPU is required to individually control the first and second memories, so that a complicated control program is needed. Further in this case, it is impossible to simultaneously read out the data from the first and second memories, resulting in the reduction of the data processing speed.
In another printing apparatus, a memory is used for storing the printing data indicative of the rotational angular position of the printing wheel and the impact force of the printing hammer that correspond to each character code. The CPU reads out the printing data corresponding to the input character code from this memory and simultaneously supplies the rotation angle data and impact force data included in this printing data to the printing wheel driver and printing hammer driver, respectively. Thus, the rotation angle data and impact force data corresponding to each character code are simultaneously read out. However, this causes the number of bits of printing data including both data to be enlarged. Since the capacity of the data bus is restricted and it is undesirable to reduce the number of bits of the rotation angle data, it is required in turn to decrease the number of bits of the impact force data. In a particular case, the impact can be merely set to strong and weak forces; therefore, the densities of the characters printed cannot be made sufficiently uniform.